Abstract P6-04-10: Components of cap-independent translation as novel targets in breast cancer

Background: The majority of cellular mRNAs are translated in a cap-dependent manner, involving ribosome assembly at 5’ 7-methylguanylate cap structures followed by scanning and initiation at a favorable AUG codon. Alternatively, mRNA structural elements termed internal ribosome entry sites (IRESs) facilitate translation in a cap-independent manner, and have been identified in mRNAs encoding many canonical cellular oncogenes, including c-MYC, c-SRC, XIAP, Aurora-A kinase, and IGF1R. IRES trans-activating factors (ITAFs) are accessory proteins that augment or inhibit translation mediated by specific IRES sequences, via binding to IRES structures and/ or other translational machinery. In addition, conversion of ribosomal RNA (rRNA) uracil bases to pseudouracil enhances IRES-mediated translation.

Methods: Analysis of publically available microarray datasets of breast cancer and normal breast tissue clinical specimens revealed that expression of several ITAFs is upregulated at the mRNA level in malignant tissues compared to normal controls. mRNAs encoding the ITAFs polypyrimidine tract binding protein 1 (PTBP1), splicing factor proline/ glutamine rich (SFPQ), poly-RC binding protein 2 (PCBP2), and interleukin enhancer binding factor 2 (ILF2, also NF45) were significantly upregulated (p < 0.05), as well as mRNA encoding the dyskeratosis congenita 1 (DKC1) rRNA-modifying enzyme. Independent analysis of an 855 human breast tumor dataset revealed that high mRNA expression of DKC1 and ILF2 are enriched in basal-like breast tumors compared to other intrinsic subtypes (t-test, p<0.01). Kaplan-Meier analyses revealed that high expression of DKC1 or ILF2 mRNAs were both significantly associated with decreased relapse-free survival duration (p = 0.0007 and p = 0.002, respectively).

To investigate the biological impact of ITAF and DKC1 silencing, PTBP1, PCBP2, SFPQ, and DKC1 knockdown was accomplished using pGIPZ and pTRIPZ lentiviral shRNA vectors. Silencing of these genes and concomitant reduction in protein levels (measured by western blot) led to significant proliferation impairment in MDA-MB-231, MDA-MB-436, and MCF7 breast cancer cells in culture, using Alamar Blue assay. In addition, 4T1 mouse mammary carcinoma cells express DKC1, PTBP1 and SFPQ, and may serve as a useful model in immunocompetent mice.

Conclusions and future directions: Future experiments will include investigation of protein-level expression in archival human specimens using immunohistochemistry, as well as investigation of the effects of ITAF/ DKC1 silencing in human xenografts using NOD/ SCID mice. Based on their increased expression in malignant breast tissues and activity in translation of oncoproteins, cellular ITAF genes and DKC1 gene may represent novel therapeutic targets for intervention. In particular, the increased expression of DKC1 enzyme and ILF2 in basal-like breast cancers implies a possible therapeutic opportunity in triple-negative breast cancers.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P6-04-10.

Abstract P5-08-03: In vitro resistance to ERBB2-targeted therapies does not bestow cross-resistance to antibody dependent cellular cytotoxicity

Background:

The advent of ERBB2-directed therapies, including trastuzumab and lapatinib, has changed the clinical management of ERBB2+ breast cancer and improved patient outcomes. However, both de novo and acquired resistance to ERBB2-targeting agents remain significant clinical problems; thus, it is important to understand the mechanisms that tumor cells use to resist and/ or escape ERBB2-directed therapeutic agents. A growing body of evidence supports the role of immune effector cells in trastuzumab-induced tumor cell lysis in vivo, which is hypothesized to occur through antibody dependent cellular cytotoxicity (ADCC) mediated by natural killer cells bearing FC gamma receptors. Existing in vitro models of trastuzumab and lapatinib resistance are limited in that they are most often generated by incubating tumor cells with drug alone, outside the context of the host immune system. Consequently, the impact of in vitro generated drug resistance on ADCC susceptibility has not been defined. In this study, we tested existing trastuzumab and lapatinib resistant breast cancer cell lines for ADCC sensitivity.

Materials and Methods:

The ERBB2 amplified breast cancer cell lines BT474 and SKBR3, which are sensitive to trastuzumab-mediated ADCC, were selected for trastuzumab and lapatinib resistance. Drug resistant cells were generated by serial culture in the presence of escalating doses of trastuzumab and/or lapatinib until complete tolerance was acquired at clinically achievable concentrations (100μg/ml trastuzumab and 2.6μM lapatinib). Drug sensitivity was assessed by Alamar Blue assay. Cell resistance to trastuzumab-mediated ADCC was measured by Calcein-AM release assay, using 1μg/ml antibody concentration and four different effector target ratios (20:1, 10:1, 5:1, and 1:1), with a minimum of five replicates. Human peripheral blood lymphocytes freshly isolated from buffy coat were used as effector cells.

Results and Discussion:

Neither BT474 nor SKBR3 cells with acquired resistance to single agent trastuzumab (HerR), lapatinib (LapR), or both in combination (DualR) demonstrated cross-resistance to effector cell-mediated ADCC at any of the E:T ratios tested. At the highest E:T ratio tested (20:1), trastuzumab-induced ADCC of control BT474 cells resulted in 61.92% cell lysis (95% CI = 3.97), compared to 64.97% lysis for BT-HerR cells (95% CI = 2.87, Student's t-test p > 0.1). Similarly, BT-LapR and DualR cell lysis was 58.13% and 63.66%, respectively (95% CI = 2.62 and 6.57, Student's t-test p > 0.1). Additionally, trastuzumab-induced ADCC of control SKBR3 cells resulted in 89.98% cell lysis (95% CI = 4.29), compared to 93.53% lysis for SK-HerR cells (95% CI = 0.81, Student's t-test p > 0.1). SK-LapR and DualR cell lysis was 94.81% and 92.09%, respectively (95% CI = 0.6 and 2.66, Student's t-test p > 0.1). Our results indicate the importance of incorporating immune effector cells to in vitro models of trastuzumab resistance. Accordingly, we have begun modeling ADCC resistance in vitro to further investigate the relationship between targeted antibody therapies, effector cell-mediated cytolysis, and mechanisms of tumor immune escape.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-08-03.

Truncated p110 ERBB2 induces mammary epithelial cell migration, invasion and orthotopic xenograft formation, and is associated with loss of phosphorylated STAT5

Truncated-ERBB2 isoforms (t-ERBB2s), resulting from receptor proteolysis or alternative translation of the ERBB2 mRNA, exist in a subset of human breast tumors. t-ERBB2s lack the receptor extracellular domain targeted by therapeutic anti-ERBB2 antibodies and antibody–drug conjugates, including trastuzumab, trastuzumab-DM1 and pertuzumab. In clinical studies, expression of t-ERBB2 in breast tumors correlates with metastasis as well as trastuzumab resistance. By using a novel immuno-microarray method, we detect a significant t-ERBB2 fraction in 18 of 31 (58%) of immunohistochemistry (IHC)3+ ERBB2+ human tumor specimens, and further show that t-ERBB2 isoforms are phosphorylated in a subset of IHC3+ samples (10 of 31, 32%). We investigated t-ERBB2 biological activity via engineered expression of full-length and truncated ERBB2 isoforms in human mammary epithelial cells (HMECs), including HMEC and MCF10A cells. Expression of p110 t-ERBB2, but not p95m (m=membrane, also 648CTF) or intracellular ERBB2s, significantly enhanced cell migration and invasion in multiple cell types. In addition, only expression of the p110 isoform led to human breast epithelial cell (HMLE) xenograft formation in vivo. Expression of t-ERBB2s did not result in hyperactivation of the phosphoinositide kinase-3/AKT or mitogen-activated protein kinase signaling pathways in these cells; rather, phosphoproteomic array profiling revealed attenuation of phosphorylated signal transducer and activator of transcription 5 (STAT5) in p110-t-ERBB2-expressing cells compared to controls. Short hairpin-mediated silencing of STAT5 phenocopied p110-t-ERBB2-driven cell migration and invasion, while expression of constitutively active STAT5 reversed these effects. Thus, we provide novel evidence that (1) expression of p110 t-ERBB2 is sufficient for full transformation of HMEC, yielding in vivo xenograft formation, and (2) truncated p110 t-ERBB2 expression is associated with decreased phosphorylation of STAT5.

PD01-09: Identifying Novel Mechanisms of Resistance to Lapatinib in ERBB2+ Breast Cancer Cells through Whole Genome Mutational Analysis

Background: Overexpression of the epidermal growth factor receptor ERBB2 (HER2) is found in 20% of human breast cancers. Therapies targeting ERBB2 including trastuzumab and lapatinib have significantly improved the outlook for women with ERBB2+ breast cancer. However, resistance to these agents occurs frequently and remains a significant clinical problem. In the case of lapatinib resistance, the mechanism(s) of resistance remain poorly understood, since the current proposed rationale thought to limit lapatinib's anti-tumor effects has been difficult to reconcile with clinical data. Therefore, we hypothesize that novel mechanisms of resistance could be identified by mapping genomic variations in ERBB2+ cells with acquired resistance to lapatinib. The identification of such mutations may provide insights into mechanisms of resistance and may indicate therapeutic strategies to overcome lapatinib resistance in ERBB2+ breast cancer.

Material and Methods: SKBR3 breast cancer cells resistant to lapatinib were generated through serial passage by exposure of drug sensitive parental SKBR3 cells to increasing concentrations of lapatinib up to the peak plasma concentration observed in human subjects (2.6 uM (SK-lapR)). Multiple signaling pathways in lapatinib sensitive and resistant cells were interrogated by Reverse Phase Protein Array (RPPA) and western blot analysis. To identify genome wide somatic mutations, the Exome of lapatinib resistant and sensitive SKBR3 cells was sequenced utilizing next generation deep sequencing. Following exclusion of germline variants, the acquired gene mutations in lapatinib resistant SKBR3 cells were confirmed by DNA re-sequencing of PCR amplified DNA segments.

Results and Discussion: Analysis of activated signaling pathways in lapatinib resistant and sensitive SKBR3 cells did not confirm any of the previously proposed mechanisms of resistance. In particular, these cells show no activation of AKT or alternative receptor tyrosine kinases such as IGF-IR, ERBB3 or c-Met. However they exhibit sustained activation of mTORC1 and ERK1/2, as well as phosphorylation of STAT3, STAT5, rpS6 and CREB. Initial sequence analysis of exome and transcriptome reveals the presence of 76 single nucleotide variants/Indels differing between sensitive and resistant cells with 34/76 validated as true mutations present in the genome of lapatinib resistant SKBR3 cells, including mutations in LATS2, MAP3K5, SMAD3 and PDGFRA. This is the first exome sequence analysis to be reported which defines a drug resistant phenotype in ERBB2+ breast cancer. Ongoing work includes investigation of mutations as drug resistance mediators and analysis of copy number variations and gene fusions/translocations to systematically search for molecular alterations, with the goal of providing a rationale for the design of new combination therapies aimed at lapatinib resistance for ERBB2+ breast cancer.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr PD01-09.

P2-01-25: Truncated p110 ERBB2 (CTF611) Increases Migration and Invasion of Breast Epithelial Cells by Inhibiting STAT5b Activation

Background: Truncated ERBB2 receptors are present in a subset of human ERBB2+ amplified/overexpressing breast tumors, and are associated with trastuzumab resistance, metastasis, and poor clinical prognosis. However, whether truncated ERBB2 receptors are drivers of metastasis has not been well defined. In this study, we examined effects of full-length (p185) and truncated (p110) ERBB2 on the migration and invasion of human mammary epithelial cells, including HMLE and MCF10A cells.

Material and Methods: Recombinant p185 and p110 ERBB2 were stably expressed in human mammary epithelial cells (HMLE) and MCF10A cells via retroviral vector. Expression of comparable levels of p185 and p110 in cells was confirmed by western blot. The phosphorylation states of downstream signaling proteins including STAT5 were assayed via phosphoproteomics and Collaborative Enzyme Enhanced Reactive (CEER™) immunoassay. The effects of the p110 constructs on cell migration and invasion were investigated by transwell assays. shRNA-encoding lentivirus was used for specific silencing of STAT5b in HMLE cells, and STAT5b silencing was confirmed at the protein level using western blot.

Results and Discussion: Expression of p110 ERBB2 increased cell migration (HMLE, p = 0.04; MCF10A, p< 0.01) and invasion (HMLE, p= 0.03) when compared to expression of p185. Furthermore, expression of p110 in HMLE cells was associated with reduced phosphorylation of STAT5b. shRNA mediated silencing of STAT5b was sufficient to increase the migration (p < 0.01) and invasion of HMLE cells, phenocopying the p110 driven effects on HMLE cells. In clinical studies, loss of activated STAT5 protein correlates with breast cancer progression and is a negative predictor of survival. By analyzing publicly available gene expression datasets, we found that STAT5b mRNA expression is also significantly decreased in breast cancer compared to normal breast tissues in several studies, as well as in ERBB2 amplified vs. nonamplified samples. To our knowledge, this is the first reported perturbation of STAT signaling by truncated ERBB2 receptor, and suggests a mechanism by which truncated p110 ERBB2 (CTF611) increases migration and invasion of breast epithelial cells. This study extends the available data regarding STAT5 loss in breast cancer progression.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P2-01-25.

Spawning dynamics and biomass estimates of an anchovy Engraulis australis population in contrasting gulf and shelf environments

The spawning biomass of Australian anchovy Engraulis australis in gulf and shelf waters of South Australia was compared using the daily egg production method (DEPM). The total survey area was 128 700 km2 with recorded spawning areas in gulf and shelf waters of 4898 and 44 618 km2, respectively. High egg densities in the warm, shallow gulf waters were produced by small, young (<1 year old) E. australis that spawned relatively small batches of eggs (c. 855) approximately every 3 days. In cooler, deeper shelf waters, where larger, older E. australis are found, lower egg densities occurred despite individuals producing much larger batches of eggs (c. 15,572) approximately every 7 days. In shelf waters, the highest densities were recorded at inshore sampling stations. Spawning appeared to peak between 0000 and 0100 hours. Females were more abundant than males in samples from both gulf and shelf waters with sex ratios of 0.61 and 0.56, respectively. The spawning biomass of E. australis in shelf waters was 101 522 t, whereas the estimate for gulf waters was 25 374 t. Due to the differences in mean size of the spawning females, however, c. 6x10(9)E. australis were present in each region. The results support the hypothesis that variability in habitat conditions may directly influence E. australis reproduction. A large reserve of young fish in the relatively stable gulf environment may increase the resilience of the E. australis population in South Australia to unfavourable interannual changes in offshore environmental conditions.

Simian varicella virus gene 61 encodes a viral transactivator but is non-essential for in vitro replication

Simian varicella virus (SVV) is closely related to varicella-zoster virus (VZV), the causative agent of chickenpox and shingles. The SVV and VZV gene 61 polypeptides are homologs of the HSV-1 ICP0, a viral transactivator which appears to play a role in viral latency and reactivation. In this study, the molecular properties of the SVV 61 were characterized. The SVV open reading frame (ORF) 61 encodes a 54.1-kDa polypeptide with 37% amino acid identity to the VZV 61. Homology to the HSV-1 ICP-0 is limited to a conserved RING finger motif at the amino terminus of the protein. A nuclear localization sequence (nls) at the carboxy-terminus directs the SVV 61 to the cell nucleus, while a SVV 61nls(-) mutant is confined to the cell cytoplasm. The SVV 61 transactivates its own promoter as well as SVV immediate early (IE, ORF 62), early (ORFs 28 and 29), and late (ORF 68) gene promoters in transfected Vero cells. The RING finger and nls motifs are required for efficient SVV 61 transactivation. The SVV 61 has no effect on the ability of the major SVV transactivator (IE62) to induce SVV promoters. Generation and propagation of a SVV gene 61 deletion mutant demonstrated that the SVV 61 is non-essential for in vitro replication. SVV gene 61 is expressed in liver, lung, and neural ganglia of infected monkeys during acute simian varicella.

Psychotherapeutic injury: reshaping the implied contract as an alternative to malpractice

Despite the enormous number of Americans who seek psychiatric aid for their emotional problems, malpractice actions against psychiatrists are surprisingly rare. In this Article, Professors Feldman and Ward suggest that this stage of affairs is caused not by the extraordinary competence of the psychiatric profession, but rather by the particularly severe legal obstacles that confront injured psychiatric patients. The elements of the traditional tort cause of action--especially causation--are not easily proved by plaintiffs claiming psychiatric injury. Moreover, recent cases show that courts are growing even more unsympathetic to those patients who suffer most grievously from unscrupulous psychiatrists. To remedy this problem, the authors reach to the historical origins of medical malpractice liability, and advocate the revival of an implied contract to treat with skill and care. By imposing a fiduciary obligation on the psychiatrist in the performance of this contract, the authors overcome the obstacles of proof that arise from traditional tort law. This alternative approach should bring a new balance to the law of psychiatric malpractice, in which aggrieved patients will be compensated for thier injuries, but innovative practitioners will not be unduly deterred from medical experimentation.